I ran into a problem today that had me really scratching my head for several hours.
I created several files in Partworks but the Shopbot program displayed a "Runtime Error 91" and then quit each time I tried to load the file. When I stepped through the file line by line I received a "runtime error 424"
I was able to clear up the problem by reinstalling the shopbot program but the real problem was related to the fact that I had relocated the SBParts folder from the C root of my harddrive to another folder.
This is waht really caused the error - just an FYI for those who might encounter this annoying user caused problem.